how to clean a PDP8/A, dishwasher?

From: Pete Turnbull <>
Date: Sat Dec 15 06:48:24 2001

On Dec 14, 23:47, Gunther Schadow wrote:

> But first I need to give this thing a good cleaning. A friend
> has assured me that there's nothing better than the dishwasher,
> with the exception of big capacitors and, what about magnetic
> core memory? So, how should I clean the RAM cards? How the
> DC power supply units?

NOT the core! If you need to clean the core, my suggestion would be to
immerse it in a washing-up basin with tepid water and a little soap or
washing-up detergent, and *gently* swish it about a little. Then rinse
twice, let it drain, and dry off gently. Don't use compressed air or

> If I put the other stuff in the dishwasher, I know there should
> be no detergent and no heat dry. But what about the rinsing
> aid, do I have to pump this out of the reservoir?

I don't think the detergent will do any harm, providing it's not too
caustic, but avoid excessively hot water and high-temperature drying.
 Before you use the dishwasher, check for switches etc that might not take
kindly to being immersed in soapy water, and either carefully remove them
(taking careful note of where they go) and relays (don't wash relays).
 Also check for any labels that will be damaged or which might come off and
end up where you don't want them. The rinse aid won't do any harm at all,
in fact it wil help the water drain off (it's just a wetting agent).

> I heard of another method using hand-washing first, then drying
> and finally a bath in Isopropanol. Is that what I should do
> with the core memory cards?

Yes, see above, but omit the IPA.

When I cleaned my PDP-8/E recently, I put all the boards except the core in
the dishwasher, along with the front panel circuit board (I removed the
LEDs first, since they were in bi-pin sockets), over-the-top connectors,
and the two backplanes. I ran it on the usual cycle, with detergent and
rinse aid.

When I took the boards out, I blew off the remaining water (some tends to
stay under ICs) with compressed air, and gave anything that might harbour
water (DIP switches, panel switches) a good dose of iso-propyl alcohol,
which I then drained/blew off. The IPA mixes with the remaining water and
helps to remove it; the air removes the last traces of IPA. Finally I
treated all the switches to a small dose of low-residue switch

Similar treatment for the backplanes and connectors, except it's hard to
get the last of the water/IPA out so I let them stand upright in front of a
hair drier on a low heat setting for a couple of hours while I got on with
other things.

The PSU was too big for the dishwasher, and I wouldn't have wanted the
transformer in there anyway. The 8/E has a linear supply with a big
transformer; the 8/A has a switcher, I think. Anyway, I took off the side
panel, removed the fans, relay, and fuse carriers (carefully noting how
they were wired). I sprayed it with enzymatic cleaner (it was smelly) and
detergent mixed with water in a spray bottle to dissolve the muck, left it
to sit for a few minutes, and then rinsed it out with the garden hose (low
pressure!) trying to avoid getting too much water into the transformer.
 Then I drained it out, and used most of a 500g aerosol of IPA to flush out
the water, and compressed air to remove the residue, especially in the
connectors. I let it stand in a warm dry room overnight before powering it
up; I figured there might still be dampness in nooks and crannies in the
transformer, and I didn't want to take chances.

If you have small parts that need washed, then they can go in the cutlery
basket in the dishwasher providing they're heavy enough not to jump out
(metal brackets for example) or in a strong mesh bag in the dishwasher.
 For more delicate things you can tie them in a pillowcase and put them in
the washing machine. I use the pillowcase/washing machine for keytops,
cartridge cases, etc.

Most of the foam in my 8/E was past redemption, so I stripped it off with a
wallpaper stripping knife and replaced it with "high-density" upholstery
foam about 3/8" thick -- not the really high density stuff that seems to be
made of lumps of recylcled stuff, just the stuff used to pad seats. I
cleaned off the old glue and stuck the new foam on with spray glue, after
masking off the area to spray (like you would for spray paint). The foam
under the backplanes was OK, so it went in the (clothes) washing machine on
a hot wash.

> Finally, finally, I noticed that the cards are all slightly
> bent from being kept in a horizontal position. They are sagging
> a little, like a hammock. Would that be a cause of concern
> in the long run? Should I mount the chassis in an upright
> position in the future?

Not unless they're so badly warped that things might short between cards.
 Some of mine were warped when I got them, and don't seem to have suffered.

> any other things I should know?

Use a pen torch to look in the backplane slots for any rubbish the
dishwasher might not remove (paperclips, cruddy foam, etc). Do make sure
everything is dry before you power them up (or even reassemble them). Do
make a note of where and how everything you remove goes back. I thought
all the LEDs in my panel were the same way up; they weren't and it took me
half an hour (without the circuit diagrams) to get them all the right way

I find it helpful to put the screws from each section or panel or whatever
into a separate ziplock bag or a dish; there are always some missing and it
helps figure out what goes where, how many are needed, and what lengths
they should be when you come to reassemble it all. Check the fans rotate
freely; I always relubricate bronze bearing types with light machine oil.

I have a few toggle-in programs I've collected or modified for first-time
confidence testing, like the inchworm program and a couple of serial port
testers (continuously write character to console; echo console, etc).

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Sat Dec 15 2001 - 06:48:24 GMT

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